1.4 Getting Started

This book assumes that the reader is familiar with the basic physics of electricity and with basic circuit theory. There are a few ideas that need to be stressed before we discuss circuit board design. A review is a good idea and I hope that the reader will take the time to read these few paragraphs.¹ The intent is to stress concepts. Simple equations will be presented because they are the clearest way to state relationships.

In an isolated uncharged conductor there is a balance of charge. In every atom, the inner protons carry a positive charge equal to the negative charge on the electrons. This balance is extremely precise. In a conductor, electrons can easily move between atoms. We call this motion current. The percentage of available electrons that partake in electrical circuit activity is so small that it is hard to describe it in useful terms. The ratio is like that of a teaspoon of sand to miles of beach.

The forces that exist between electrons are not easily imagined. Consider that 1% of the electrons in a human being are free to interact with the same number of electrons on a second person. The force between the charges would be enough to lift the earth out of orbit. It is obvious from this fact that the number of electrons involved in any electrical activity in our circuits is indeed very small. It is hard to realize that this immense electrical force is involved in current flow.

The protons are so well shielded inside the atom that they do not partake in normal circuit activity. In the circuits we will consider, most of the electrons move on the surface of conductors. To start, consider a group of extra electrons placed on a conductor. These electrons are free to move between atoms. The forces between these “free” electrons cause them to move apart as far as they can go. On a conductor, they assume a position that stores the least amount of potential energy. On an isolated sphere, they end up spaced uniformly on the entire outer surface.

An accumulation of added electrons is called a negative charge. A depletion of electrons from a conductor is called a positive charge. These pseudopositive charges attract electrons and move just like electrons. When a pseudopositive charge meets an electron, they are canceled. In other words, the electron is accepted by an atom to fill in its outer shell. In most of our discussions we will discuss the motion of charges and the direction of current flow. The polarity of surface charges will not be discussed.